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 $245.26   5.281%   $258.2122   $258.21   $258.20   $258.20  
  Purchase #2 $46.27   12.192%   $51.9112   $51.91   $51.90   $51.90  
  Purchase #3 $230.68   7.556%   $248.1102   $248.11   $248.10   $248.10  
  Purchase #4 $90.25   4.623%   $94.4223   $94.42   $94.40   $94.40  
  Purchase #5 $234.41   4.214%   $244.288   $244.29   $244.30   $244.30  
  Purchase #6 $187.32   6.392%   $199.2935   $199.29   $199.30   $199.30  
  Purchase #7 $70.86   5.367%   $74.6631   $74.66   $74.65   $74.70  
  7 purchase totals = $1,105.05       $1,170.9005   $1,170.89   $1,170.85   $1,170.90