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 $221.95   3.651%   $230.0534   $230.05   $230.05   $230.10  
  Purchase #2 $241.85   12.243%   $271.4597   $271.46   $271.45   $271.50  
  Purchase #3 $194.48   9.782%   $213.504   $213.50   $213.50   $213.50  
  Purchase #4 $205.55   3.427%   $212.5942   $212.59   $212.60   $212.60  
  Purchase #5 $107.82   7.249%   $115.6359   $115.64   $115.65   $115.60  
  Purchase #6 $184.37   12.847%   $208.056   $208.06   $208.05   $208.10  
  Purchase #7 $242.77   8.133%   $262.5145   $262.51   $262.50   $262.50  
  7 purchase totals = $1,398.79       $1,513.8177   $1,513.81   $1,513.80   $1,513.90