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 $95.87   11.107%   $106.5183   $106.52   $106.50   $106.50  
  Purchase #2 $170.80   12.208%   $191.6513   $191.65   $191.65   $191.70  
  Purchase #3 $129.71   12.134%   $145.449   $145.45   $145.45   $145.40  
  Purchase #4 $237.72   3.637%   $246.3659   $246.37   $246.35   $246.40  
  Purchase #5 $99.58   3.661%   $103.2256   $103.23   $103.25   $103.20  
  Purchase #6 $223.86   5.413%   $235.9775   $235.98   $236.00   $236.00  
  Purchase #7 $116.72   11.728%   $130.4089   $130.41   $130.40   $130.40  
  7 purchase totals = $1,074.26       $1,159.5965   $1,159.61   $1,159.60   $1,159.60