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 $207.86   5.809%   $219.9346   $219.93   $219.95   $219.90  
  Purchase #2 $23.51   12.189%   $26.3756   $26.38   $26.40   $26.40  
  Purchase #3 $136.44   4.812%   $143.0055   $143.01   $143.00   $143.00  
  Purchase #4 $159.82   8.433%   $173.2976   $173.30   $173.30   $173.30  
  Purchase #5 $46.46   8.612%   $50.4611   $50.46   $50.45   $50.50  
  Purchase #6 $119.65   8.219%   $129.484   $129.48   $129.50   $129.50  
  Purchase #7 $245.86   11.146%   $273.2636   $273.26   $273.25   $273.30  
  7 purchase totals = $939.60       $1,015.8220   $1,015.82   $1,015.85   $1,015.90