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 $68.27   11.546%   $76.1525   $76.15   $76.15   $76.20  
  Purchase #2 $113.36   7.541%   $121.9085   $121.91   $121.90   $121.90  
  Purchase #3 $212.41   7.422%   $228.1751   $228.18   $228.20   $228.20  
  Purchase #4 $138.84   11.812%   $155.2398   $155.24   $155.25   $155.20  
  Purchase #5 $106.36   6.614%   $113.3947   $113.39   $113.40   $113.40  
  Purchase #6 $193.67   5.559%   $204.4361   $204.44   $204.45   $204.40  
  Purchase #7 $68.92   11.756%   $77.0222   $77.02   $77.00   $77.00  
  7 purchase totals = $901.83       $976.3289   $976.33   $976.35   $976.30