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 $60.54   12.214%   $67.9344   $67.93   $67.95   $67.90  
  Purchase #2 $209.95   8.121%   $227   $227.00   $227.00   $227.00  
  Purchase #3 $109.76   3.646%   $113.7618   $113.76   $113.75   $113.80  
  Purchase #4 $165.56   9.837%   $181.8461   $181.85   $181.85   $181.80  
  Purchase #5 $128.57   12.234%   $144.2993   $144.30   $144.30   $144.30  
  Purchase #6 $159.84   3.138%   $164.8558   $164.86   $164.85   $164.90  
  Purchase #7 $90.62   7.363%   $97.2924   $97.29   $97.30   $97.30  
  7 purchase totals = $924.84       $996.9898   $996.99   $997.00   $997.00