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 $28.67   12.823%   $32.3464   $32.35   $32.35   $32.30  
  Purchase #2 $205.98   13.349%   $233.4763   $233.48   $233.50   $233.50  
  Purchase #3 $87.56   4.259%   $91.2892   $91.29   $91.30   $91.30  
  Purchase #4 $141.53   3.203%   $146.0632   $146.06   $146.05   $146.10  
  Purchase #5 $112.97   6.589%   $120.4136   $120.41   $120.40   $120.40  
  Purchase #6 $57.98   11.325%   $64.5462   $64.55   $64.55   $64.50  
  Purchase #7 $91.66   11.541%   $102.2385   $102.24   $102.25   $102.20  
  7 purchase totals = $726.35       $790.3734   $790.38   $790.40   $790.30