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 $232.99   13.766%   $265.0634   $265.06   $265.05   $265.10  
  Purchase #2 $123.45   12.309%   $138.6455   $138.65   $138.65   $138.60  
  Purchase #3 $49.29   12.616%   $55.5084   $55.51   $55.50   $55.50  
  Purchase #4 $204.49   5.235%   $215.1951   $215.20   $215.20   $215.20  
  Purchase #5 $53.75   9.229%   $58.7106   $58.71   $58.70   $58.70  
  Purchase #6 $108.90   13.534%   $123.6385   $123.64   $123.65   $123.60  
  Purchase #7 $51.90   8.488%   $56.3053   $56.31   $56.30   $56.30  
  7 purchase totals = $824.77       $913.0668   $913.08   $913.05   $913.00