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 $162.43   13.462%   $184.2963   $184.30   $184.30   $184.30  
  Purchase #2 $220.51   4.307%   $230.0074   $230.01   $230.00   $230.00  
  Purchase #3 $153.59   9.600%   $168.3346   $168.33   $168.35   $168.30  
  Purchase #4 $107.87   12.634%   $121.4983   $121.50   $121.50   $121.50  
  Purchase #5 $95.50   7.734%   $102.886   $102.89   $102.90   $102.90  
  Purchase #6 $14.64   12.195%   $16.4253   $16.43   $16.45   $16.40  
  Purchase #7 $153.51   3.117%   $158.2949   $158.29   $158.30   $158.30  
  7 purchase totals = $908.05       $981.7428   $981.75   $981.80   $981.70