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 $247.69   11.427%   $275.9935   $275.99   $276.00   $276.00  
  Purchase #2 $242.73   11.555%   $270.7775   $270.78   $270.80   $270.80  
  Purchase #3 $245.84   3.264%   $253.8642   $253.86   $253.85   $253.90  
  Purchase #4 $193.89   10.116%   $213.5039   $213.50   $213.50   $213.50  
  Purchase #5 $70.95   10.732%   $78.5644   $78.56   $78.55   $78.60  
  Purchase #6 $28.47   12.326%   $31.9792   $31.98   $32.00   $32.00  
  Purchase #7 $23.88   10.317%   $26.3437   $26.34   $26.35   $26.30  
  7 purchase totals = $1,053.45       $1,151.0264   $1,151.01   $1,151.05   $1,151.10