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 $52.76   9.494%   $57.769   $57.77   $57.75   $57.80  
  Purchase #2 $216.70   10.144%   $238.682   $238.68   $238.70   $238.70  
  Purchase #3 $207.39   10.541%   $229.251   $229.25   $229.25   $229.30  
  Purchase #4 $190.72   5.858%   $201.8924   $201.89   $201.90   $201.90  
  Purchase #5 $93.37   12.518%   $105.0581   $105.06   $105.05   $105.10  
  Purchase #6 $198.49   5.787%   $209.9766   $209.98   $210.00   $210.00  
  Purchase #7 $112.84   4.504%   $117.9223   $117.92   $117.90   $117.90  
  7 purchase totals = $1,072.27       $1,160.5514   $1,160.55   $1,160.55   $1,160.70