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 $58.48   11.110%   $64.9771   $64.98   $65.00   $65.00  
  Purchase #2 $189.34   6.438%   $201.5297   $201.53   $201.55   $201.50  
  Purchase #3 $124.51   11.645%   $139.0092   $139.01   $139.00   $139.00  
  Purchase #4 $195.89   4.169%   $204.0567   $204.06   $204.05   $204.10  
  Purchase #5 $235.65   13.458%   $267.3638   $267.36   $267.35   $267.40  
  Purchase #6 $124.89   11.433%   $139.1687   $139.17   $139.15   $139.20  
  Purchase #7 $6.43   10.600%   $7.1116   $7.11   $7.10   $7.10  
  7 purchase totals = $935.19       $1,023.2168   $1,023.22   $1,023.20   $1,023.30