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 $66.38   11.244%   $73.8438   $73.84   $73.85   $73.80  
  Purchase #2 $147.62   9.138%   $161.1095   $161.11   $161.10   $161.10  
  Purchase #3 $73.35   6.399%   $78.0437   $78.04   $78.05   $78.00  
  Purchase #4 $58.28   4.627%   $60.9766   $60.98   $61.00   $61.00  
  Purchase #5 $46.61   6.673%   $49.7203   $49.72   $49.70   $49.70  
  Purchase #6 $242.73   8.128%   $262.4591   $262.46   $262.45   $262.50  
  Purchase #7 $244.70   11.430%   $272.6692   $272.67   $272.65   $272.70  
  7 purchase totals = $879.67       $958.8222   $958.82   $958.80   $958.80