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 $244.97   10.219%   $270.0035   $270.00   $270.00   $270.00  
  Purchase #2 $68.30   6.677%   $72.8604   $72.86   $72.85   $72.90  
  Purchase #3 $189.57   4.192%   $197.5168   $197.52   $197.50   $197.50  
  Purchase #4 $240.88   12.522%   $271.043   $271.04   $271.05   $271.00  
  Purchase #5 $213.97   6.600%   $228.092   $228.09   $228.10   $228.10  
  Purchase #6 $221.92   3.564%   $229.8292   $229.83   $229.85   $229.80  
  Purchase #7 $86.54   6.626%   $92.2741   $92.27   $92.25   $92.30  
  7 purchase totals = $1,266.15       $1,361.6190   $1,361.61   $1,361.60   $1,361.60