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 $67.87   10.194%   $74.7887   $74.79   $74.80   $74.80  
  Purchase #2 $168.75   10.594%   $186.6274   $186.63   $186.65   $186.60  
  Purchase #3 $222.26   8.173%   $240.4253   $240.43   $240.45   $240.40  
  Purchase #4 $26.84   3.542%   $27.7907   $27.79   $27.80   $27.80  
  Purchase #5 $119.54   11.799%   $133.6445   $133.64   $133.65   $133.60  
  Purchase #6 $142.43   10.590%   $157.5133   $157.51   $157.50   $157.50  
  Purchase #7 $246.85   13.529%   $280.2463   $280.25   $280.25   $280.20  
  7 purchase totals = $994.54       $1,101.0362   $1,101.04   $1,101.10   $1,100.90