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 $175.86   10.777%   $194.8124   $194.81   $194.80   $194.80  
  Purchase #2 $128.68   5.131%   $135.2826   $135.28   $135.30   $135.30  
  Purchase #3 $151.45   12.127%   $169.8163   $169.82   $169.80   $169.80  
  Purchase #4 $33.62   5.852%   $35.5874   $35.59   $35.60   $35.60  
  Purchase #5 $58.60   4.130%   $61.0202   $61.02   $61.00   $61.00  
  Purchase #6 $194.60   9.346%   $212.7873   $212.79   $212.80   $212.80  
  Purchase #7 $148.99   10.598%   $164.78   $164.78   $164.80   $164.80  
  7 purchase totals = $891.80       $974.0862   $974.09   $974.10   $974.10