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 $87.46   7.391%   $93.9242   $93.92   $93.90   $93.90  
  Purchase #2 $199.40   5.463%   $210.2932   $210.29   $210.30   $210.30  
  Purchase #3 $175.44   13.844%   $199.7279   $199.73   $199.75   $199.70  
  Purchase #4 $72.81   10.710%   $80.608   $80.61   $80.60   $80.60  
  Purchase #5 $107.37   9.320%   $117.3769   $117.38   $117.40   $117.40  
  Purchase #6 $197.93   11.555%   $220.8008   $220.80   $220.80   $220.80  
  Purchase #7 $131.53   5.420%   $138.6589   $138.66   $138.65   $138.70  
  7 purchase totals = $971.94       $1,061.3899   $1,061.39   $1,061.40   $1,061.40