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 $82.33   13.208%   $93.2041   $93.20   $93.20   $93.20  
  Purchase #2 $194.59   12.660%   $219.2251   $219.23   $219.25   $219.20  
  Purchase #3 $137.89   8.166%   $149.1501   $149.15   $149.15   $149.20  
  Purchase #4 $153.37   11.667%   $171.2637   $171.26   $171.25   $171.30  
  Purchase #5 $248.67   13.582%   $282.4444   $282.44   $282.45   $282.40  
  Purchase #6 $38.41   7.227%   $41.1859   $41.19   $41.20   $41.20  
  Purchase #7 $224.45   13.536%   $254.8316   $254.83   $254.85   $254.80  
  7 purchase totals = $1,079.71       $1,211.3049   $1,211.30   $1,211.35   $1,211.30