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 $61.99   5.808%   $65.5904   $65.59   $65.60   $65.60  
  Purchase #2 $104.92   10.761%   $116.2104   $116.21   $116.20   $116.20  
  Purchase #3 $185.34   11.330%   $206.339   $206.34   $206.35   $206.30  
  Purchase #4 $76.57   9.732%   $84.0218   $84.02   $84.00   $84.00  
  Purchase #5 $187.89   9.742%   $206.1942   $206.19   $206.20   $206.20  
  Purchase #6 $141.36   11.337%   $157.386   $157.39   $157.40   $157.40  
  Purchase #7 $245.43   3.107%   $253.0555   $253.06   $253.05   $253.10  
  7 purchase totals = $1,003.50       $1,088.7973   $1,088.80   $1,088.80   $1,088.80