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 $181.55   7.376%   $194.9411   $194.94   $194.95   $194.90  
  Purchase #2 $229.29   3.423%   $237.1386   $237.14   $237.15   $237.10  
  Purchase #3 $94.92   7.239%   $101.7913   $101.79   $101.80   $101.80  
  Purchase #4 $24.59   8.296%   $26.63   $26.63   $26.65   $26.60  
  Purchase #5 $110.65   10.214%   $121.9518   $121.95   $121.95   $122.00  
  Purchase #6 $159.86   4.127%   $166.4574   $166.46   $166.45   $166.50  
  Purchase #7 $85.25   12.612%   $96.0017   $96.00   $96.00   $96.00  
  7 purchase totals = $886.11       $944.9119   $944.91   $944.95   $944.90