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 $51.86   3.172%   $53.505   $53.51   $53.50   $53.50  
  Purchase #2 $181.41   11.325%   $201.9547   $201.95   $201.95   $202.00  
  Purchase #3 $177.63   9.417%   $194.3574   $194.36   $194.35   $194.40  
  Purchase #4 $235.41   8.785%   $256.0908   $256.09   $256.10   $256.10  
  Purchase #5 $158.48   7.502%   $170.3692   $170.37   $170.35   $170.40  
  Purchase #6 $184.29   4.104%   $191.8533   $191.85   $191.85   $191.90  
  Purchase #7 $247.75   11.550%   $276.3651   $276.37   $276.35   $276.40  
  7 purchase totals = $1,236.83       $1,344.4955   $1,344.50   $1,344.45   $1,344.70