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 $242.37   8.327%   $262.5521   $262.55   $262.55   $262.60  
  Purchase #2 $156.41   6.129%   $165.9964   $166.00   $166.00   $166.00  
  Purchase #3 $108.75   4.397%   $113.5317   $113.53   $113.55   $113.50  
  Purchase #4 $238.70   12.298%   $268.0553   $268.06   $268.05   $268.10  
  Purchase #5 $238.48   4.257%   $248.6321   $248.63   $248.65   $248.60  
  Purchase #6 $150.40   13.578%   $170.8213   $170.82   $170.80   $170.80  
  Purchase #7 $30.32   11.479%   $33.8004   $33.80   $33.80   $33.80  
  7 purchase totals = $1,165.43       $1,263.3893   $1,263.39   $1,263.40   $1,263.40