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 $94.54   6.350%   $100.5433   $100.54   $100.55   $100.50  
  Purchase #2 $72.58   3.128%   $74.8503   $74.85   $74.85   $74.90  
  Purchase #3 $160.97   7.682%   $173.3357   $173.34   $173.35   $173.30  
  Purchase #4 $97.43   6.736%   $103.9929   $103.99   $104.00   $104.00  
  Purchase #5 $124.64   6.262%   $132.445   $132.45   $132.45   $132.40  
  Purchase #6 $224.53   9.588%   $246.0579   $246.06   $246.05   $246.10  
  Purchase #7 $205.38   11.753%   $229.5183   $229.52   $229.50   $229.50  
  7 purchase totals = $980.07       $1,060.7434   $1,060.75   $1,060.75   $1,060.70