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 $55.48   11.802%   $62.0277   $62.03   $62.05   $62.00  
  Purchase #2 $8.93   4.109%   $9.2969   $9.30   $9.30   $9.30  
  Purchase #3 $194.65   9.262%   $212.6785   $212.68   $212.70   $212.70  
  Purchase #4 $178.53   13.399%   $202.4512   $202.45   $202.45   $202.50  
  Purchase #5 $76.47   7.617%   $82.2947   $82.29   $82.30   $82.30  
  Purchase #6 $157.70   12.269%   $177.0482   $177.05   $177.05   $177.00  
  Purchase #7 $141.47   4.475%   $147.8008   $147.80   $147.80   $147.80  
  7 purchase totals = $813.23       $893.5980   $893.60   $893.65   $893.60