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 $211.36   3.228%   $218.1827   $218.18   $218.20   $218.20  
  Purchase #2 $49.89   3.800%   $51.7858   $51.79   $51.80   $51.80  
  Purchase #3 $14.79   9.185%   $16.1485   $16.15   $16.15   $16.10  
  Purchase #4 $142.32   7.735%   $153.3285   $153.33   $153.35   $153.30  
  Purchase #5 $146.65   13.609%   $166.6076   $166.61   $166.60   $166.60  
  Purchase #6 $91.37   4.481%   $95.4643   $95.46   $95.45   $95.50  
  Purchase #7 $238.46   8.607%   $258.9843   $258.98   $259.00   $259.00  
  7 purchase totals = $894.84       $960.5017   $960.50   $960.55   $960.50