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 $208.96   12.123%   $234.2922   $234.29   $234.30   $234.30  
  Purchase #2 $221.93   6.502%   $236.3599   $236.36   $236.35   $236.40  
  Purchase #3 $14.82   7.727%   $15.9651   $15.97   $15.95   $16.00  
  Purchase #4 $78.72   12.120%   $88.2609   $88.26   $88.25   $88.30  
  Purchase #5 $204.62   9.425%   $223.9054   $223.91   $223.90   $223.90  
  Purchase #6 $239.36   12.583%   $269.4787   $269.48   $269.50   $269.50  
  Purchase #7 $246.49   7.390%   $264.7056   $264.71   $264.70   $264.70  
  7 purchase totals = $1,214.90       $1,332.9678   $1,332.98   $1,332.95   $1,333.10