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 $41.77   5.539%   $44.0836   $44.08   $44.10   $44.10  
  Purchase #2 $238.49   10.355%   $263.1856   $263.19   $263.20   $263.20  
  Purchase #3 $80.71   4.833%   $84.6107   $84.61   $84.60   $84.60  
  Purchase #4 $211.32   10.440%   $233.3818   $233.38   $233.40   $233.40  
  Purchase #5 $142.60   12.284%   $160.117   $160.12   $160.10   $160.10  
  Purchase #6 $72.33   12.758%   $81.5579   $81.56   $81.55   $81.60  
  Purchase #7 $93.97   3.317%   $97.087   $97.09   $97.10   $97.10  
  7 purchase totals = $881.19       $964.0236   $964.03   $964.05   $964.10