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 $186.79   3.808%   $193.903   $193.90   $193.90   $193.90  
  Purchase #2 $22.98   9.397%   $25.1394   $25.14   $25.15   $25.10  
  Purchase #3 $237.26   12.535%   $267.0005   $267.00   $267.00   $267.00  
  Purchase #4 $172.71   5.504%   $182.216   $182.22   $182.20   $182.20  
  Purchase #5 $208.66   5.281%   $219.6793   $219.68   $219.70   $219.70  
  Purchase #6 $98.26   5.122%   $103.2929   $103.29   $103.30   $103.30  
  Purchase #7 $61.83   12.237%   $69.3961   $69.40   $69.40   $69.40  
  7 purchase totals = $988.49       $1,060.6272   $1,060.63   $1,060.65   $1,060.60