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 $238.46   10.311%   $263.0476   $263.05   $263.05   $263.00  
  Purchase #2 $16.75   8.242%   $18.1305   $18.13   $18.15   $18.10  
  Purchase #3 $180.89   10.421%   $199.7405   $199.74   $199.75   $199.70  
  Purchase #4 $69.66   4.308%   $72.661   $72.66   $72.65   $72.70  
  Purchase #5 $163.80   3.310%   $169.2218   $169.22   $169.20   $169.20  
  Purchase #6 $207.89   9.595%   $227.837   $227.84   $227.85   $227.80  
  Purchase #7 $117.45   6.475%   $125.0549   $125.05   $125.05   $125.10  
  7 purchase totals = $994.90       $1,075.6933   $1,075.69   $1,075.70   $1,075.60