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 $180.95   8.207%   $195.8006   $195.80   $195.80   $195.80  
  Purchase #2 $229.59   9.645%   $251.734   $251.73   $251.75   $251.70  
  Purchase #3 $59.35   7.661%   $63.8968   $63.90   $63.90   $63.90  
  Purchase #4 $103.46   12.696%   $116.5953   $116.60   $116.60   $116.60  
  Purchase #5 $23.47   6.280%   $24.9439   $24.94   $24.95   $24.90  
  Purchase #6 $232.41   4.770%   $243.496   $243.50   $243.50   $243.50  
  Purchase #7 $61.69   8.383%   $66.8615   $66.86   $66.85   $66.90  
  7 purchase totals = $890.92       $963.3281   $963.33   $963.35   $963.30