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 $223.43   5.842%   $236.4828   $236.48   $236.50   $236.50  
  Purchase #2 $110.56   10.740%   $122.4341   $122.43   $122.45   $122.40  
  Purchase #3 $70.36   10.559%   $77.7893   $77.79   $77.80   $77.80  
  Purchase #4 $226.94   5.590%   $239.6259   $239.63   $239.65   $239.60  
  Purchase #5 $194.29   12.292%   $218.1721   $218.17   $218.15   $218.20  
  Purchase #6 $89.99   6.763%   $96.076   $96.08   $96.10   $96.10  
  Purchase #7 $119.75   13.602%   $136.0384   $136.04   $136.05   $136.00  
  7 purchase totals = $1,035.32       $1,126.6186   $1,126.62   $1,126.70   $1,126.60