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 $129.41   10.123%   $142.5102   $142.51   $142.50   $142.50  
  Purchase #2 $89.83   11.506%   $100.1658   $100.17   $100.15   $100.20  
  Purchase #3 $121.61   7.126%   $130.2759   $130.28   $130.30   $130.30  
  Purchase #4 $233.69   3.828%   $242.6357   $242.64   $242.65   $242.60  
  Purchase #5 $248.27   13.620%   $282.0844   $282.08   $282.10   $282.10  
  Purchase #6 $183.38   11.770%   $204.9638   $204.96   $204.95   $205.00  
  Purchase #7 $39.46   5.279%   $41.5431   $41.54   $41.55   $41.50  
  7 purchase totals = $1,045.65       $1,144.1789   $1,144.18   $1,144.20   $1,144.20