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 $245.31   3.441%   $253.7511   $253.75   $253.75   $253.80  
  Purchase #2 $101.79   11.653%   $113.6516   $113.65   $113.65   $113.70  
  Purchase #3 $176.72   11.577%   $197.1789   $197.18   $197.20   $197.20  
  Purchase #4 $157.51   5.654%   $166.4156   $166.42   $166.40   $166.40  
  Purchase #5 $235.30   9.320%   $257.23   $257.23   $257.25   $257.20  
  Purchase #6 $6.96   8.735%   $7.568   $7.57   $7.55   $7.60  
  Purchase #7 $56.94   4.697%   $59.6145   $59.61   $59.60   $59.60  
  7 purchase totals = $980.53       $1,055.4097   $1,055.41   $1,055.40   $1,055.50