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 $135.82   6.527%   $144.685   $144.69   $144.70   $144.70  
  Purchase #2 $117.75   5.676%   $124.4335   $124.43   $124.45   $124.40  
  Purchase #3 $139.56   10.315%   $153.9556   $153.96   $153.95   $154.00  
  Purchase #4 $247.96   5.757%   $262.2351   $262.24   $262.25   $262.20  
  Purchase #5 $47.80   5.236%   $50.3028   $50.30   $50.30   $50.30  
  Purchase #6 $163.97   11.266%   $182.4429   $182.44   $182.45   $182.40  
  Purchase #7 $156.47   13.460%   $177.5309   $177.53   $177.55   $177.50  
  7 purchase totals = $1,009.33       $1,095.5858   $1,095.59   $1,095.65   $1,095.50