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 $81.63   6.650%   $87.0584   $87.06   $87.05   $87.10  
  Purchase #2 $163.66   7.248%   $175.5221   $175.52   $175.50   $175.50  
  Purchase #3 $158.42   13.331%   $179.539   $179.54   $179.55   $179.50  
  Purchase #4 $143.26   4.685%   $149.9717   $149.97   $149.95   $150.00  
  Purchase #5 $132.56   9.572%   $145.2486   $145.25   $145.25   $145.20  
  Purchase #6 $191.50   8.723%   $208.2045   $208.20   $208.20   $208.20  
  Purchase #7 $65.48   4.623%   $68.5071   $68.51   $68.50   $68.50  
  7 purchase totals = $936.51       $1,014.0514   $1,014.05   $1,014.00   $1,014.00