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 $81.51   6.402%   $86.7283   $86.73   $86.75   $86.70  
  Purchase #2 $115.77   5.684%   $122.3504   $122.35   $122.35   $122.40  
  Purchase #3 $51.31   3.267%   $52.9863   $52.99   $53.00   $53.00  
  Purchase #4 $201.76   12.402%   $226.7823   $226.78   $226.80   $226.80  
  Purchase #5 $113.44   12.805%   $127.966   $127.97   $127.95   $128.00  
  Purchase #6 $88.40   3.833%   $91.7884   $91.79   $91.80   $91.80  
  Purchase #7 $51.74   5.576%   $54.625   $54.63   $54.65   $54.60  
  7 purchase totals = $703.93       $763.2267   $763.24   $763.30   $763.30