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 $242.91   8.129%   $262.6562   $262.66   $262.65   $262.70  
  Purchase #2 $230.27   5.348%   $242.5848   $242.58   $242.60   $242.60  
  Purchase #3 $88.93   8.688%   $96.6562   $96.66   $96.65   $96.70  
  Purchase #4 $209.80   11.131%   $233.1528   $233.15   $233.15   $233.20  
  Purchase #5 $149.66   6.480%   $159.358   $159.36   $159.35   $159.40  
  Purchase #6 $126.35   4.613%   $132.1785   $132.18   $132.20   $132.20  
  Purchase #7 $136.31   6.732%   $145.4864   $145.49   $145.50   $145.50  
  7 purchase totals = $1,184.23       $1,272.0729   $1,272.08   $1,272.10   $1,272.30