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 $124.97   9.633%   $137.0084   $137.01   $137.00   $137.00  
  Purchase #2 $154.83   13.360%   $175.5153   $175.52   $175.50   $175.50  
  Purchase #3 $208.51   10.274%   $229.9323   $229.93   $229.95   $229.90  
  Purchase #4 $99.44   7.535%   $106.9328   $106.93   $106.95   $106.90  
  Purchase #5 $215.43   5.214%   $226.6625   $226.66   $226.65   $226.70  
  Purchase #6 $10.64   5.263%   $11.2   $11.20   $11.20   $11.20  
  Purchase #7 $50.69   3.190%   $52.307   $52.31   $52.30   $52.30  
  7 purchase totals = $864.51       $939.5583   $939.56   $939.55   $939.50