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 $195.55   3.709%   $202.8029   $202.80   $202.80   $202.80  
  Purchase #2 $113.63   3.592%   $117.7116   $117.71   $117.70   $117.70  
  Purchase #3 $125.94   5.270%   $132.577   $132.58   $132.60   $132.60  
  Purchase #4 $233.36   6.118%   $247.637   $247.64   $247.65   $247.60  
  Purchase #5 $114.43   5.523%   $120.75   $120.75   $120.75   $120.80  
  Purchase #6 $106.59   4.579%   $111.4708   $111.47   $111.45   $111.50  
  Purchase #7 $43.60   13.314%   $49.4049   $49.40   $49.40   $49.40  
  7 purchase totals = $933.10       $982.3542   $982.35   $982.35   $982.40