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 $85.51   11.376%   $95.2376   $95.24   $95.25   $95.20  
  Purchase #2 $145.44   3.630%   $150.7195   $150.72   $150.70   $150.70  
  Purchase #3 $114.76   10.131%   $126.3863   $126.39   $126.40   $126.40  
  Purchase #4 $63.37   4.265%   $66.0727   $66.07   $66.05   $66.10  
  Purchase #5 $100.72   5.490%   $106.2495   $106.25   $106.25   $106.20  
  Purchase #6 $237.86   5.745%   $251.5251   $251.53   $251.55   $251.50  
  Purchase #7 $192.33   12.612%   $216.5867   $216.59   $216.60   $216.60  
  7 purchase totals = $939.99       $1,012.7774   $1,012.79   $1,012.80   $1,012.70