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 $180.44   7.842%   $194.5901   $194.59   $194.60   $194.60  
  Purchase #2 $82.74   13.363%   $93.7965   $93.80   $93.80   $93.80  
  Purchase #3 $205.54   12.491%   $231.214   $231.21   $231.20   $231.20  
  Purchase #4 $72.90   8.265%   $78.9252   $78.93   $78.95   $78.90  
  Purchase #5 $124.81   6.437%   $132.844   $132.84   $132.85   $132.80  
  Purchase #6 $241.37   12.116%   $270.6144   $270.61   $270.60   $270.60  
  Purchase #7 $161.60   4.571%   $168.9867   $168.99   $169.00   $169.00  
  7 purchase totals = $1,069.40       $1,170.9709   $1,170.97   $1,171.00   $1,170.90