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 $191.56   8.227%   $207.3196   $207.32   $207.30   $207.30  
  Purchase #2 $103.75   4.541%   $108.4613   $108.46   $108.45   $108.50  
  Purchase #3 $108.36   5.499%   $114.3187   $114.32   $114.30   $114.30  
  Purchase #4 $33.38   5.460%   $35.2025   $35.20   $35.20   $35.20  
  Purchase #5 $217.42   6.766%   $232.1306   $232.13   $232.15   $232.10  
  Purchase #6 $88.89   11.688%   $99.2795   $99.28   $99.30   $99.30  
  Purchase #7 $234.93   7.689%   $252.9938   $252.99   $253.00   $253.00  
  7 purchase totals = $978.29       $1,049.7060   $1,049.70   $1,049.70   $1,049.70