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 $193.86   7.549%   $208.4945   $208.49   $208.50   $208.50  
  Purchase #2 $121.42   10.826%   $134.5649   $134.56   $134.55   $134.60  
  Purchase #3 $117.27   9.804%   $128.7672   $128.77   $128.75   $128.80  
  Purchase #4 $219.84   8.282%   $238.0471   $238.05   $238.05   $238.00  
  Purchase #5 $67.87   8.790%   $73.8358   $73.84   $73.85   $73.80  
  Purchase #6 $201.51   4.309%   $210.1931   $210.19   $210.20   $210.20  
  Purchase #7 $200.30   7.199%   $214.7196   $214.72   $214.70   $214.70  
  7 purchase totals = $1,122.07       $1,208.6222   $1,208.62   $1,208.60   $1,208.60