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 $222.93   13.709%   $253.4915   $253.49   $253.50   $253.50  
  Purchase #2 $189.67   3.641%   $196.5759   $196.58   $196.60   $196.60  
  Purchase #3 $152.65   11.217%   $169.7728   $169.77   $169.75   $169.80  
  Purchase #4 $64.37   6.734%   $68.7047   $68.70   $68.70   $68.70  
  Purchase #5 $126.92   13.632%   $144.2217   $144.22   $144.20   $144.20  
  Purchase #6 $238.49   3.708%   $247.3332   $247.33   $247.35   $247.30  
  Purchase #7 $119.39   5.146%   $125.5338   $125.53   $125.55   $125.50  
  7 purchase totals = $1,114.42       $1,205.6336   $1,205.62   $1,205.65   $1,205.60