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 $134.86   11.744%   $150.698   $150.70   $150.70   $150.70  
  Purchase #2 $237.52   8.710%   $258.208   $258.21   $258.20   $258.20  
  Purchase #3 $146.25   9.830%   $160.6264   $160.63   $160.65   $160.60  
  Purchase #4 $118.92   11.193%   $132.2307   $132.23   $132.25   $132.20  
  Purchase #5 $194.44   7.490%   $209.0036   $209.00   $209.00   $209.00  
  Purchase #6 $221.51   11.282%   $246.5008   $246.50   $246.50   $246.50  
  Purchase #7 $188.32   6.856%   $201.2312   $201.23   $201.25   $201.20  
  7 purchase totals = $1,241.82       $1,358.4987   $1,358.50   $1,358.55   $1,358.40