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 $210.99   12.158%   $236.6422   $236.64   $236.65   $236.60  
  Purchase #2 $101.50   9.316%   $110.9557   $110.96   $110.95   $111.00  
  Purchase #3 $30.65   6.275%   $32.5733   $32.57   $32.55   $32.60  
  Purchase #4 $189.93   3.444%   $196.4712   $196.47   $196.45   $196.50  
  Purchase #5 $238.37   13.532%   $270.6262   $270.63   $270.65   $270.60  
  Purchase #6 $115.25   5.719%   $121.8411   $121.84   $121.85   $121.80  
  Purchase #7 $79.30   7.767%   $85.4592   $85.46   $85.45   $85.50  
  7 purchase totals = $965.99       $1,054.5689   $1,054.57   $1,054.55   $1,054.60