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 $110.82   3.474%   $114.6699   $114.67   $114.65   $114.70  
  Purchase #2 $97.30   11.256%   $108.2521   $108.25   $108.25   $108.30  
  Purchase #3 $160.98   9.413%   $176.133   $176.13   $176.15   $176.10  
  Purchase #4 $241.31   5.339%   $254.1935   $254.19   $254.20   $254.20  
  Purchase #5 $49.98   11.777%   $55.8661   $55.87   $55.85   $55.90  
  Purchase #6 $149.70   8.741%   $162.7853   $162.79   $162.80   $162.80  
  Purchase #7 $175.51   13.532%   $199.26   $199.26   $199.25   $199.30  
  7 purchase totals = $985.60       $1,071.1599   $1,071.16   $1,071.15   $1,071.30