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 $238.55   12.211%   $267.6793   $267.68   $267.70   $267.70  
  Purchase #2 $54.60   5.322%   $57.5058   $57.51   $57.50   $57.50  
  Purchase #3 $247.28   8.821%   $269.0926   $269.09   $269.10   $269.10  
  Purchase #4 $239.29   11.811%   $267.5525   $267.55   $267.55   $267.60  
  Purchase #5 $116.87   7.489%   $125.6224   $125.62   $125.60   $125.60  
  Purchase #6 $26.79   8.734%   $29.1298   $29.13   $29.15   $29.10  
  Purchase #7 $36.98   9.359%   $40.441   $40.44   $40.45   $40.40  
  7 purchase totals = $960.36       $1,057.0234   $1,057.02   $1,057.05   $1,057.00