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 $239.32   10.506%   $264.463   $264.46   $264.45   $264.50  
  Purchase #2 $54.76   10.205%   $60.3483   $60.35   $60.35   $60.30  
  Purchase #3 $111.94   12.845%   $126.3187   $126.32   $126.30   $126.30  
  Purchase #4 $240.94   6.858%   $257.4637   $257.46   $257.45   $257.50  
  Purchase #5 $203.45   8.570%   $220.8857   $220.89   $220.90   $220.90  
  Purchase #6 $57.80   4.522%   $60.4137   $60.41   $60.40   $60.40  
  Purchase #7 $25.97   11.396%   $28.9295   $28.93   $28.95   $28.90  
  7 purchase totals = $934.18       $1,018.8226   $1,018.82   $1,018.80   $1,018.80