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 $240.82   5.553%   $254.1927   $254.19   $254.20   $254.20  
  Purchase #2 $93.88   11.390%   $104.5729   $104.57   $104.55   $104.60  
  Purchase #3 $225.68   4.265%   $235.3053   $235.31   $235.30   $235.30  
  Purchase #4 $139.45   7.191%   $149.4778   $149.48   $149.50   $149.50  
  Purchase #5 $146.42   7.609%   $157.5611   $157.56   $157.55   $157.60  
  Purchase #6 $202.72   3.500%   $209.8152   $209.82   $209.80   $209.80  
  Purchase #7 $41.42   11.467%   $46.1696   $46.17   $46.15   $46.20  
  7 purchase totals = $1,090.39       $1,157.0946   $1,157.10   $1,157.05   $1,157.20