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 $57.67   9.771%   $63.3049   $63.30   $63.30   $63.30  
  Purchase #2 $216.66   12.275%   $243.255   $243.26   $243.25   $243.30  
  Purchase #3 $185.43   7.592%   $199.5078   $199.51   $199.50   $199.50  
  Purchase #4 $151.91   13.304%   $172.1201   $172.12   $172.10   $172.10  
  Purchase #5 $188.73   12.658%   $212.6194   $212.62   $212.60   $212.60  
  Purchase #6 $60.70   13.872%   $69.1203   $69.12   $69.10   $69.10  
  Purchase #7 $122.85   10.206%   $135.3881   $135.39   $135.40   $135.40  
  7 purchase totals = $983.95       $1,095.3156   $1,095.32   $1,095.25   $1,095.30