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 $33.92   13.186%   $38.3927   $38.39   $38.40   $38.40  
  Purchase #2 $59.85   6.506%   $63.7438   $63.74   $63.75   $63.70  
  Purchase #3 $44.38   3.789%   $46.0616   $46.06   $46.05   $46.10  
  Purchase #4 $24.82   7.361%   $26.647   $26.65   $26.65   $26.60  
  Purchase #5 $247.61   10.653%   $273.9879   $273.99   $274.00   $274.00  
  Purchase #6 $34.49   7.142%   $36.9533   $36.95   $36.95   $37.00  
  Purchase #7 $204.31   3.812%   $212.0983   $212.10   $212.10   $212.10  
  7 purchase totals = $649.38       $697.8846   $697.88   $697.90   $697.90