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 $53.78   4.713%   $56.3147   $56.31   $56.30   $56.30  
  Purchase #2 $241.28   11.156%   $268.1972   $268.20   $268.20   $268.20  
  Purchase #3 $182.89   3.431%   $189.165   $189.17   $189.15   $189.20  
  Purchase #4 $51.96   4.557%   $54.3278   $54.33   $54.35   $54.30  
  Purchase #5 $191.78   7.432%   $206.0331   $206.03   $206.05   $206.00  
  Purchase #6 $212.70   3.720%   $220.6124   $220.61   $220.60   $220.60  
  Purchase #7 $234.85   13.614%   $266.8225   $266.82   $266.80   $266.80  
  7 purchase totals = $1,169.24       $1,261.4727   $1,261.47   $1,261.45   $1,261.40