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 $36.88   13.693%   $41.93   $41.93   $41.95   $41.90  
  Purchase #2 $146.44   8.561%   $158.9767   $158.98   $159.00   $159.00  
  Purchase #3 $36.54   5.336%   $38.4898   $38.49   $38.50   $38.50  
  Purchase #4 $204.45   3.686%   $211.986   $211.99   $212.00   $212.00  
  Purchase #5 $86.67   9.260%   $94.6956   $94.70   $94.70   $94.70  
  Purchase #6 $234.75   8.271%   $254.1662   $254.17   $254.15   $254.20  
  Purchase #7 $240.27   13.262%   $272.1346   $272.13   $272.15   $272.10  
  7 purchase totals = $986.00       $1,072.3789   $1,072.39   $1,072.45   $1,072.40