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 $23.93   8.245%   $25.903   $25.90   $25.90   $25.90  
  Purchase #2 $34.28   5.421%   $36.1383   $36.14   $36.15   $36.10  
  Purchase #3 $211.39   7.746%   $227.7643   $227.76   $227.75   $227.80  
  Purchase #4 $96.68   7.778%   $104.1998   $104.20   $104.20   $104.20  
  Purchase #5 $213.91   4.459%   $223.4482   $223.45   $223.45   $223.40  
  Purchase #6 $234.61   3.670%   $243.2202   $243.22   $243.20   $243.20  
  Purchase #7 $126.95   13.438%   $144.0095   $144.01   $144.00   $144.00  
  7 purchase totals = $941.75       $1,004.6833   $1,004.68   $1,004.65   $1,004.60