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 $158.91   6.762%   $169.6555   $169.66   $169.65   $169.70  
  Purchase #2 $44.94   8.357%   $48.6956   $48.70   $48.70   $48.70  
  Purchase #3 $68.28   6.671%   $72.835   $72.84   $72.85   $72.80  
  Purchase #4 $249.55   4.429%   $260.6026   $260.60   $260.60   $260.60  
  Purchase #5 $60.78   6.471%   $64.7131   $64.71   $64.70   $64.70  
  Purchase #6 $113.43   4.479%   $118.5105   $118.51   $118.50   $118.50  
  Purchase #7 $45.64   6.807%   $48.7467   $48.75   $48.75   $48.70  
  7 purchase totals = $741.53       $783.7590   $783.77   $783.75   $783.70