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 $224.66   8.287%   $243.2776   $243.28   $243.30   $243.30  
  Purchase #2 $210.81   3.582%   $218.3612   $218.36   $218.35   $218.40  
  Purchase #3 $157.34   6.629%   $167.7701   $167.77   $167.75   $167.80  
  Purchase #4 $198.81   8.239%   $215.19   $215.19   $215.20   $215.20  
  Purchase #5 $55.38   12.860%   $62.5019   $62.50   $62.50   $62.50  
  Purchase #6 $173.53   10.850%   $192.358   $192.36   $192.35   $192.40  
  Purchase #7 $41.46   3.173%   $42.7755   $42.78   $42.80   $42.80  
  7 purchase totals = $1,061.99       $1,142.2343   $1,142.24   $1,142.25   $1,142.40