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 $204.29   10.229%   $225.1868   $225.19   $225.20   $225.20  
  Purchase #2 $124.64   6.837%   $133.1616   $133.16   $133.15   $133.20  
  Purchase #3 $25.48   8.557%   $27.6603   $27.66   $27.65   $27.70  
  Purchase #4 $233.39   12.646%   $262.9045   $262.90   $262.90   $262.90  
  Purchase #5 $94.26   13.827%   $107.2933   $107.29   $107.30   $107.30  
  Purchase #6 $120.60   3.272%   $124.546   $124.55   $124.55   $124.50  
  Purchase #7 $117.77   7.215%   $126.2671   $126.27   $126.25   $126.30  
  7 purchase totals = $920.43       $1,007.0196   $1,007.02   $1,007.00   $1,007.10