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 $85.47   11.825%   $95.5768   $95.58   $95.60   $95.60  
  Purchase #2 $145.64   7.567%   $156.6606   $156.66   $156.65   $156.70  
  Purchase #3 $129.82   10.130%   $142.9708   $142.97   $142.95   $143.00  
  Purchase #4 $228.56   3.212%   $235.9013   $235.90   $235.90   $235.90  
  Purchase #5 $17.91   10.840%   $19.8514   $19.85   $19.85   $19.90  
  Purchase #6 $216.27   6.853%   $231.091   $231.09   $231.10   $231.10  
  Purchase #7 $28.68   9.572%   $31.4252   $31.43   $31.45   $31.40  
  7 purchase totals = $852.35       $913.4771   $913.48   $913.50   $913.60