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 $89.80   5.323%   $94.5801   $94.58   $94.60   $94.60  
  Purchase #2 $18.91   3.872%   $19.6422   $19.64   $19.65   $19.60  
  Purchase #3 $136.67   7.296%   $146.6414   $146.64   $146.65   $146.60  
  Purchase #4 $160.68   7.824%   $173.2516   $173.25   $173.25   $173.30  
  Purchase #5 $191.72   3.714%   $198.8405   $198.84   $198.85   $198.80  
  Purchase #6 $176.95   9.402%   $193.5868   $193.59   $193.60   $193.60  
  Purchase #7 $5.55   9.173%   $6.0591   $6.06   $6.05   $6.10  
  7 purchase totals = $780.28       $832.6017   $832.60   $832.65   $832.60