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 $102.85   10.466%   $113.6143   $113.61   $113.60   $113.60  
  Purchase #2 $95.44   9.350%   $104.3636   $104.36   $104.35   $104.40  
  Purchase #3 $67.70   12.435%   $76.1185   $76.12   $76.10   $76.10  
  Purchase #4 $51.48   7.840%   $55.516   $55.52   $55.50   $55.50  
  Purchase #5 $206.74   13.322%   $234.2819   $234.28   $234.30   $234.30  
  Purchase #6 $96.97   8.281%   $105.0001   $105.00   $105.00   $105.00  
  Purchase #7 $101.83   7.273%   $109.2361   $109.24   $109.25   $109.20  
  7 purchase totals = $723.01       $798.1305   $798.13   $798.10   $798.10