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 $179.62   8.399%   $194.7063   $194.71   $194.70   $194.70  
  Purchase #2 $228.97   9.440%   $250.5848   $250.58   $250.60   $250.60  
  Purchase #3 $172.61   4.193%   $179.8475   $179.85   $179.85   $179.80  
  Purchase #4 $33.82   9.279%   $36.9582   $36.96   $36.95   $37.00  
  Purchase #5 $13.55   5.138%   $14.2462   $14.25   $14.25   $14.20  
  Purchase #6 $235.46   12.863%   $265.7472   $265.75   $265.75   $265.70  
  Purchase #7 $96.78   5.174%   $101.7874   $101.79   $101.80   $101.80  
  7 purchase totals = $960.81       $1,043.8776   $1,043.89   $1,043.90   $1,043.80