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 $158.38   9.852%   $173.9836   $173.98   $174.00   $174.00  
  Purchase #2 $203.61   13.567%   $231.2338   $231.23   $231.25   $231.20  
  Purchase #3 $167.49   12.594%   $188.5837   $188.58   $188.60   $188.60  
  Purchase #4 $236.67   7.729%   $254.9622   $254.96   $254.95   $255.00  
  Purchase #5 $30.83   11.644%   $34.4198   $34.42   $34.40   $34.40  
  Purchase #6 $140.70   3.805%   $146.0536   $146.05   $146.05   $146.10  
  Purchase #7 $235.87   3.372%   $243.8235   $243.82   $243.80   $243.80  
  7 purchase totals = $1,173.55       $1,273.0602   $1,273.04   $1,273.05   $1,273.10