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 $87.91   6.162%   $93.327   $93.33   $93.35   $93.30  
  Purchase #2 $204.68   3.303%   $211.4406   $211.44   $211.45   $211.40  
  Purchase #3 $32.31   12.459%   $36.3355   $36.34   $36.35   $36.30  
  Purchase #4 $148.97   9.271%   $162.781   $162.78   $162.80   $162.80  
  Purchase #5 $198.39   4.684%   $207.6826   $207.68   $207.70   $207.70  
  Purchase #6 $176.83   8.758%   $192.3168   $192.32   $192.30   $192.30  
  Purchase #7 $225.80   13.354%   $255.9533   $255.95   $255.95   $256.00  
  7 purchase totals = $1,074.89       $1,159.8368   $1,159.84   $1,159.90   $1,159.80