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 $206.97   9.342%   $226.3051   $226.31   $226.30   $226.30  
  Purchase #2 $118.76   11.173%   $132.0291   $132.03   $132.05   $132.00  
  Purchase #3 $163.33   10.186%   $179.9668   $179.97   $179.95   $180.00  
  Purchase #4 $92.35   13.128%   $104.4737   $104.47   $104.45   $104.50  
  Purchase #5 $89.39   11.408%   $99.5876   $99.59   $99.60   $99.60  
  Purchase #6 $191.42   9.556%   $209.7121   $209.71   $209.70   $209.70  
  Purchase #7 $235.74   3.165%   $243.2012   $243.20   $243.20   $243.20  
  7 purchase totals = $1,097.96       $1,195.2756   $1,195.28   $1,195.25   $1,195.30