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 $180.83   11.817%   $202.1987   $202.20   $202.20   $202.20  
  Purchase #2 $26.51   8.299%   $28.7101   $28.71   $28.70   $28.70  
  Purchase #3 $63.50   6.335%   $67.5227   $67.52   $67.50   $67.50  
  Purchase #4 $236.39   5.263%   $248.8312   $248.83   $248.85   $248.80  
  Purchase #5 $212.26   11.861%   $237.4362   $237.44   $237.45   $237.40  
  Purchase #6 $241.91   12.461%   $272.0544   $272.05   $272.05   $272.10  
  Purchase #7 $247.72   6.861%   $264.7161   $264.72   $264.70   $264.70  
  7 purchase totals = $1,209.12       $1,321.4694   $1,321.47   $1,321.45   $1,321.40