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 $244.70   13.271%   $277.1741   $277.17   $277.15   $277.20  
  Purchase #2 $218.46   8.292%   $236.5747   $236.57   $236.55   $236.60  
  Purchase #3 $114.61   10.355%   $126.4779   $126.48   $126.50   $126.50  
  Purchase #4 $184.79   9.159%   $201.7149   $201.71   $201.70   $201.70  
  Purchase #5 $211.51   9.864%   $232.3733   $232.37   $232.35   $232.40  
  Purchase #6 $88.87   9.162%   $97.0123   $97.01   $97.00   $97.00  
  Purchase #7 $56.46   4.837%   $59.191   $59.19   $59.20   $59.20  
  7 purchase totals = $1,119.40       $1,230.5182   $1,230.50   $1,230.45   $1,230.60