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 $69.69   8.117%   $75.3467   $75.35   $75.35   $75.30  
  Purchase #2 $189.69   10.442%   $209.4974   $209.50   $209.50   $209.50  
  Purchase #3 $200.37   5.457%   $211.3042   $211.30   $211.30   $211.30  
  Purchase #4 $34.42   4.589%   $35.9995   $36.00   $36.00   $36.00  
  Purchase #5 $87.69   5.295%   $92.3332   $92.33   $92.35   $92.30  
  Purchase #6 $45.74   3.293%   $47.2462   $47.25   $47.25   $47.20  
  Purchase #7 $138.41   11.265%   $154.0019   $154.00   $154.00   $154.00  
  7 purchase totals = $766.01       $825.7291   $825.73   $825.75   $825.60