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 $182.66   11.433%   $203.5435   $203.54   $203.55   $203.50  
  Purchase #2 $110.38   5.630%   $116.5944   $116.59   $116.60   $116.60  
  Purchase #3 $7.76   4.448%   $8.1052   $8.11   $8.10   $8.10  
  Purchase #4 $206.64   5.677%   $218.371   $218.37   $218.35   $218.40  
  Purchase #5 $137.32   9.712%   $150.6565   $150.66   $150.65   $150.70  
  Purchase #6 $233.42   3.458%   $241.4917   $241.49   $241.50   $241.50  
  Purchase #7 $65.58   13.487%   $74.4248   $74.42   $74.40   $74.40  
  7 purchase totals = $943.76       $1,013.1871   $1,013.18   $1,013.15   $1,013.20