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 $92.60   12.650%   $104.3139   $104.31   $104.30   $104.30  
  Purchase #2 $161.85   4.291%   $168.795   $168.80   $168.80   $168.80  
  Purchase #3 $181.25   5.462%   $191.1499   $191.15   $191.15   $191.10  
  Purchase #4 $213.87   12.642%   $240.9074   $240.91   $240.90   $240.90  
  Purchase #5 $121.91   11.518%   $135.9516   $135.95   $135.95   $136.00  
  Purchase #6 $200.72   5.628%   $212.0165   $212.02   $212.00   $212.00  
  Purchase #7 $23.67   5.825%   $25.0488   $25.05   $25.05   $25.00  
  7 purchase totals = $995.87       $1,078.1831   $1,078.19   $1,078.15   $1,078.10