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 $59.57   6.214%   $63.2717   $63.27   $63.25   $63.30  
  Purchase #2 $203.74   12.473%   $229.1525   $229.15   $229.15   $229.20  
  Purchase #3 $218.64   3.571%   $226.4476   $226.45   $226.45   $226.40  
  Purchase #4 $207.65   7.429%   $223.0763   $223.08   $223.10   $223.10  
  Purchase #5 $104.53   11.256%   $116.2959   $116.30   $116.30   $116.30  
  Purchase #6 $197.96   9.835%   $217.4294   $217.43   $217.45   $217.40  
  Purchase #7 $19.68   10.185%   $21.6844   $21.68   $21.70   $21.70  
  7 purchase totals = $1,011.77       $1,097.3578   $1,097.36   $1,097.40   $1,097.40