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 $23.32   5.728%   $24.6558   $24.66   $24.65   $24.70  
  Purchase #2 $119.35   8.496%   $129.49   $129.49   $129.50   $129.50  
  Purchase #3 $69.37   8.675%   $75.3878   $75.39   $75.40   $75.40  
  Purchase #4 $195.92   4.865%   $205.4515   $205.45   $205.45   $205.50  
  Purchase #5 $83.43   4.339%   $87.05   $87.05   $87.05   $87.10  
  Purchase #6 $120.26   11.844%   $134.5036   $134.50   $134.50   $134.50  
  Purchase #7 $176.44   12.168%   $197.9092   $197.91   $197.90   $197.90  
  7 purchase totals = $788.09       $854.4479   $854.45   $854.45   $854.60