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 $59.68   10.857%   $66.1595   $66.16   $66.15   $66.20  
  Purchase #2 $99.92   3.643%   $103.5601   $103.56   $103.55   $103.60  
  Purchase #3 $68.93   10.459%   $76.1394   $76.14   $76.15   $76.10  
  Purchase #4 $210.35   6.310%   $223.6231   $223.62   $223.60   $223.60  
  Purchase #5 $229.41   10.223%   $252.8626   $252.86   $252.85   $252.90  
  Purchase #6 $94.53   8.644%   $102.7012   $102.70   $102.70   $102.70  
  Purchase #7 $212.32   12.383%   $238.6116   $238.61   $238.60   $238.60  
  7 purchase totals = $975.14       $1,063.6575   $1,063.65   $1,063.60   $1,063.70