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 $163.44   12.308%   $183.5562   $183.56   $183.55   $183.60  
  Purchase #2 $55.89   5.497%   $58.9623   $58.96   $58.95   $59.00  
  Purchase #3 $92.54   4.572%   $96.7709   $96.77   $96.75   $96.80  
  Purchase #4 $175.37   4.678%   $183.5738   $183.57   $183.55   $183.60  
  Purchase #5 $176.73   10.677%   $195.5995   $195.60   $195.60   $195.60  
  Purchase #6 $80.57   4.500%   $84.1957   $84.20   $84.20   $84.20  
  Purchase #7 $237.37   5.871%   $251.306   $251.31   $251.30   $251.30  
  7 purchase totals = $981.91       $1,053.9644   $1,053.97   $1,053.90   $1,054.10