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 $208.56   13.540%   $236.799   $236.80   $236.80   $236.80  
  Purchase #2 $125.99   12.831%   $142.1558   $142.16   $142.15   $142.20  
  Purchase #3 $161.52   11.789%   $180.5616   $180.56   $180.55   $180.60  
  Purchase #4 $171.31   13.470%   $194.3855   $194.39   $194.40   $194.40  
  Purchase #5 $231.37   10.222%   $255.0206   $255.02   $255.00   $255.00  
  Purchase #6 $230.50   4.461%   $240.7826   $240.78   $240.80   $240.80  
  Purchase #7 $93.26   5.226%   $98.1338   $98.13   $98.15   $98.10  
  7 purchase totals = $1,222.51       $1,347.8389   $1,347.84   $1,347.85   $1,347.90