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 $12.31   4.307%   $12.8402   $12.84   $12.85   $12.80  
  Purchase #2 $197.91   4.395%   $206.6081   $206.61   $206.60   $206.60  
  Purchase #3 $31.54   5.652%   $33.3226   $33.32   $33.30   $33.30  
  Purchase #4 $160.91   13.639%   $182.8565   $182.86   $182.85   $182.90  
  Purchase #5 $59.83   10.736%   $66.2533   $66.25   $66.25   $66.30  
  Purchase #6 $48.37   6.818%   $51.6679   $51.67   $51.65   $51.70  
  Purchase #7 $12.39   11.360%   $13.7975   $13.80   $13.80   $13.80  
  7 purchase totals = $523.26       $567.3461   $567.35   $567.30   $567.40