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 $168.79   13.310%   $191.2559   $191.26   $191.25   $191.30  
  Purchase #2 $226.88   7.811%   $244.6016   $244.60   $244.60   $244.60  
  Purchase #3 $200.90   9.168%   $219.3185   $219.32   $219.30   $219.30  
  Purchase #4 $159.53   10.598%   $176.437   $176.44   $176.45   $176.40  
  Purchase #5 $106.53   10.748%   $117.9798   $117.98   $118.00   $118.00  
  Purchase #6 $26.29   7.228%   $28.1902   $28.19   $28.20   $28.20  
  Purchase #7 $130.32   12.446%   $146.5396   $146.54   $146.55   $146.50  
  7 purchase totals = $1,019.24       $1,124.3226   $1,124.33   $1,124.35   $1,124.30