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 $35.76   8.430%   $38.7746   $38.77   $38.75   $38.80  
  Purchase #2 $238.74   11.557%   $266.3312   $266.33   $266.35   $266.30  
  Purchase #3 $46.28   11.260%   $51.4911   $51.49   $51.50   $51.50  
  Purchase #4 $248.26   11.629%   $277.1302   $277.13   $277.15   $277.10  
  Purchase #5 $170.86   11.759%   $190.9514   $190.95   $190.95   $191.00  
  Purchase #6 $14.89   9.562%   $16.3138   $16.31   $16.30   $16.30  
  Purchase #7 $233.43   4.245%   $243.3391   $243.34   $243.35   $243.30  
  7 purchase totals = $988.22       $1,084.3314   $1,084.32   $1,084.35   $1,084.30