Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $179.74   13.774%   $204.4974   $204.50   $204.50   $204.50  
  Purchase #2 $91.36   11.280%   $101.6654   $101.67   $101.65   $101.70  
  Purchase #3 $235.64   7.276%   $252.7852   $252.79   $252.80   $252.80  
  Purchase #4 $213.72   6.848%   $228.3555   $228.36   $228.35   $228.40  
  Purchase #5 $122.47   8.325%   $132.6656   $132.67   $132.65   $132.70  
  Purchase #6 $199.97   12.133%   $224.2324   $224.23   $224.25   $224.20  
  Purchase #7 $128.84   11.179%   $143.243   $143.24   $143.25   $143.20  
  7 purchase totals = $1,171.74       $1,287.4445   $1,287.46   $1,287.45   $1,287.50