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 $235.84   5.464%   $248.7263   $248.73   $248.75   $248.70  
  Purchase #2 $145.88   13.609%   $165.7328   $165.73   $165.75   $165.70  
  Purchase #3 $97.77   12.813%   $110.2973   $110.30   $110.30   $110.30  
  Purchase #4 $59.58   5.116%   $62.6281   $62.63   $62.65   $62.60  
  Purchase #5 $22.55   12.112%   $25.2813   $25.28   $25.30   $25.30  
  Purchase #6 $53.34   7.656%   $57.4237   $57.42   $57.40   $57.40  
  Purchase #7 $210.75   7.140%   $225.7976   $225.80   $225.80   $225.80  
  7 purchase totals = $825.71       $895.8871   $895.89   $895.95   $895.80