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 $95.95   8.654%   $104.2535   $104.25   $104.25   $104.30  
  Purchase #2 $161.79   8.565%   $175.6473   $175.65   $175.65   $175.60  
  Purchase #3 $6.61   13.847%   $7.5253   $7.53   $7.55   $7.50  
  Purchase #4 $116.53   10.668%   $128.9614   $128.96   $128.95   $129.00  
  Purchase #5 $63.25   6.295%   $67.2316   $67.23   $67.25   $67.20  
  Purchase #6 $47.68   9.399%   $52.1614   $52.16   $52.15   $52.20  
  Purchase #7 $176.77   10.117%   $194.6538   $194.65   $194.65   $194.70  
  7 purchase totals = $668.58       $730.4343   $730.43   $730.45   $730.50