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 $85.37   13.157%   $96.6021   $96.60   $96.60   $96.60  
  Purchase #2 $209.85   12.806%   $236.7234   $236.72   $236.70   $236.70  
  Purchase #3 $36.58   4.365%   $38.1767   $38.18   $38.20   $38.20  
  Purchase #4 $180.89   12.223%   $203.0002   $203.00   $203.00   $203.00  
  Purchase #5 $148.47   5.118%   $156.0687   $156.07   $156.05   $156.10  
  Purchase #6 $22.54   3.832%   $23.4037   $23.40   $23.40   $23.40  
  Purchase #7 $238.89   11.344%   $265.9897   $265.99   $266.00   $266.00  
  7 purchase totals = $922.59       $1,019.9645   $1,019.96   $1,019.95   $1,020.00