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 $129.42   8.696%   $140.6744   $140.67   $140.65   $140.70  
  Purchase #2 $195.92   7.788%   $211.1782   $211.18   $211.20   $211.20  
  Purchase #3 $129.78   12.309%   $145.7546   $145.75   $145.75   $145.80  
  Purchase #4 $41.70   8.698%   $45.3271   $45.33   $45.35   $45.30  
  Purchase #5 $210.97   8.753%   $229.4362   $229.44   $229.45   $229.40  
  Purchase #6 $164.75   3.662%   $170.7831   $170.78   $170.80   $170.80  
  Purchase #7 $20.41   4.323%   $21.2923   $21.29   $21.30   $21.30  
  7 purchase totals = $892.95       $964.4459   $964.44   $964.50   $964.50