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 $216.85   12.791%   $244.5873   $244.59   $244.60   $244.60  
  Purchase #2 $104.69   5.187%   $110.1203   $110.12   $110.10   $110.10  
  Purchase #3 $55.25   4.589%   $57.7854   $57.79   $57.80   $57.80  
  Purchase #4 $231.39   8.590%   $251.2664   $251.27   $251.25   $251.30  
  Purchase #5 $100.88   4.283%   $105.2007   $105.20   $105.20   $105.20  
  Purchase #6 $69.58   10.714%   $77.0348   $77.03   $77.05   $77.00  
  Purchase #7 $207.60   10.359%   $229.1053   $229.11   $229.10   $229.10  
  7 purchase totals = $986.24       $1,075.1002   $1,075.11   $1,075.10   $1,075.10