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 $86.58   10.152%   $95.3696   $95.37   $95.35   $95.40  
  Purchase #2 $229.51   7.575%   $246.8954   $246.90   $246.90   $246.90  
  Purchase #3 $45.48   5.830%   $48.1315   $48.13   $48.15   $48.10  
  Purchase #4 $189.82   3.400%   $196.2739   $196.27   $196.25   $196.30  
  Purchase #5 $24.33   8.411%   $26.3764   $26.38   $26.40   $26.40  
  Purchase #6 $23.70   9.656%   $25.9885   $25.99   $26.00   $26.00  
  Purchase #7 $164.53   10.604%   $181.9768   $181.98   $182.00   $182.00  
  7 purchase totals = $763.95       $821.0121   $821.02   $821.05   $821.10