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 $224.78   9.327%   $245.7452   $245.75   $245.75   $245.70  
  Purchase #2 $174.31   11.441%   $194.2528   $194.25   $194.25   $194.30  
  Purchase #3 $158.26   12.810%   $178.5331   $178.53   $178.55   $178.50  
  Purchase #4 $167.42   5.168%   $176.0723   $176.07   $176.05   $176.10  
  Purchase #5 $120.97   11.393%   $134.7521   $134.75   $134.75   $134.80  
  Purchase #6 $99.70   3.611%   $103.3002   $103.30   $103.30   $103.30  
  Purchase #7 $229.78   3.625%   $238.1095   $238.11   $238.10   $238.10  
  7 purchase totals = $1,175.22       $1,270.7652   $1,270.76   $1,270.75   $1,270.80