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 $212.50   13.575%   $241.3469   $241.35   $241.35   $241.30  
  Purchase #2 $72.55   4.152%   $75.5623   $75.56   $75.55   $75.60  
  Purchase #3 $24.98   11.456%   $27.8417   $27.84   $27.85   $27.80  
  Purchase #4 $92.96   13.270%   $105.2958   $105.30   $105.30   $105.30  
  Purchase #5 $230.74   10.197%   $254.2686   $254.27   $254.25   $254.30  
  Purchase #6 $163.59   13.306%   $185.3573   $185.36   $185.35   $185.40  
  Purchase #7 $244.86   7.680%   $263.6652   $263.67   $263.65   $263.70  
  7 purchase totals = $1,042.18       $1,153.3378   $1,153.35   $1,153.30   $1,153.40