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 $206.67   13.234%   $234.0207   $234.02   $234.00   $234.00  
  Purchase #2 $10.55   6.795%   $11.2669   $11.27   $11.25   $11.30  
  Purchase #3 $73.92   6.223%   $78.52   $78.52   $78.50   $78.50  
  Purchase #4 $99.95   7.341%   $107.2873   $107.29   $107.30   $107.30  
  Purchase #5 $98.30   12.150%   $110.2435   $110.24   $110.25   $110.20  
  Purchase #6 $168.73   11.796%   $188.6334   $188.63   $188.65   $188.60  
  Purchase #7 $182.46   10.801%   $202.1675   $202.17   $202.15   $202.20  
  7 purchase totals = $840.58       $932.1393   $932.14   $932.10   $932.10