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 $202.48   13.749%   $230.319   $230.32   $230.30   $230.30  
  Purchase #2 $22.35   6.718%   $23.8515   $23.85   $23.85   $23.90  
  Purchase #3 $179.33   11.783%   $200.4605   $200.46   $200.45   $200.50  
  Purchase #4 $62.60   6.803%   $66.8587   $66.86   $66.85   $66.90  
  Purchase #5 $191.87   11.586%   $214.1001   $214.10   $214.10   $214.10  
  Purchase #6 $166.87   6.701%   $178.052   $178.05   $178.05   $178.10  
  Purchase #7 $124.41   5.391%   $131.1169   $131.12   $131.10   $131.10  
  7 purchase totals = $949.91       $1,044.7587   $1,044.76   $1,044.70   $1,044.90