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 $30.72   10.558%   $33.9634   $33.96   $33.95   $34.00  
  Purchase #2 $61.88   10.458%   $68.3514   $68.35   $68.35   $68.40  
  Purchase #3 $244.39   3.788%   $253.6475   $253.65   $253.65   $253.60  
  Purchase #4 $207.51   11.871%   $232.1435   $232.14   $232.15   $232.10  
  Purchase #5 $67.35   12.794%   $75.9668   $75.97   $75.95   $76.00  
  Purchase #6 $191.92   3.262%   $198.1804   $198.18   $198.20   $198.20  
  Purchase #7 $76.37   6.167%   $81.0797   $81.08   $81.10   $81.10  
  7 purchase totals = $880.14       $943.3327   $943.33   $943.35   $943.40