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 $140.77   7.506%   $151.3362   $151.34   $151.35   $151.30  
  Purchase #2 $204.56   10.412%   $225.8588   $225.86   $225.85   $225.90  
  Purchase #3 $85.88   8.203%   $92.9247   $92.92   $92.90   $92.90  
  Purchase #4 $56.73   6.597%   $60.4725   $60.47   $60.45   $60.50  
  Purchase #5 $212.68   4.215%   $221.6445   $221.64   $221.65   $221.60  
  Purchase #6 $121.37   3.102%   $125.1349   $125.13   $125.15   $125.10  
  Purchase #7 $80.84   4.718%   $84.654   $84.65   $84.65   $84.70  
  7 purchase totals = $902.83       $962.0256   $962.01   $962.00   $962.00