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 $93.85   7.703%   $101.0793   $101.08   $101.10   $101.10  
  Purchase #2 $141.52   5.244%   $148.9413   $148.94   $148.95   $148.90  
  Purchase #3 $111.95   8.697%   $121.6863   $121.69   $121.70   $121.70  
  Purchase #4 $23.48   8.814%   $25.5495   $25.55   $25.55   $25.50  
  Purchase #5 $104.90   7.342%   $112.6018   $112.60   $112.60   $112.60  
  Purchase #6 $27.73   10.175%   $30.5515   $30.55   $30.55   $30.60  
  Purchase #7 $195.33   8.750%   $212.4214   $212.42   $212.40   $212.40  
  7 purchase totals = $698.76       $752.8311   $752.83   $752.85   $752.80