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 $63.68   7.283%   $68.3178   $68.32   $68.30   $68.30  
  Purchase #2 $241.29   4.158%   $251.3228   $251.32   $251.30   $251.30  
  Purchase #3 $209.47   13.758%   $238.2889   $238.29   $238.30   $238.30  
  Purchase #4 $56.56   11.203%   $62.8964   $62.90   $62.90   $62.90  
  Purchase #5 $115.57   3.483%   $119.5953   $119.60   $119.60   $119.60  
  Purchase #6 $118.70   9.770%   $130.297   $130.30   $130.30   $130.30  
  Purchase #7 $89.81   3.754%   $93.1815   $93.18   $93.20   $93.20  
  7 purchase totals = $895.08       $963.8997   $963.91   $963.90   $963.90