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 $66.69   10.406%   $73.6298   $73.63   $73.65   $73.60  
  Purchase #2 $145.46   3.226%   $150.1525   $150.15   $150.15   $150.20  
  Purchase #3 $241.41   12.408%   $271.3642   $271.36   $271.35   $271.40  
  Purchase #4 $175.85   12.555%   $197.928   $197.93   $197.95   $197.90  
  Purchase #5 $122.46   13.780%   $139.335   $139.34   $139.35   $139.30  
  Purchase #6 $237.95   12.457%   $267.5914   $267.59   $267.60   $267.60  
  Purchase #7 $200.88   6.358%   $213.652   $213.65   $213.65   $213.70  
  7 purchase totals = $1,190.70       $1,313.6529   $1,313.65   $1,313.70   $1,313.70