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 $89.85   9.372%   $98.2707   $98.27   $98.25   $98.30  
  Purchase #2 $126.50   8.175%   $136.8414   $136.84   $136.85   $136.80  
  Purchase #3 $120.63   6.178%   $128.0825   $128.08   $128.10   $128.10  
  Purchase #4 $167.70   11.528%   $187.0325   $187.03   $187.05   $187.00  
  Purchase #5 $246.84   8.733%   $268.3965   $268.40   $268.40   $268.40  
  Purchase #6 $245.65   4.209%   $255.9894   $255.99   $256.00   $256.00  
  Purchase #7 $207.28   6.389%   $220.5231   $220.52   $220.50   $220.50  
  7 purchase totals = $1,204.45       $1,295.1361   $1,295.13   $1,295.15   $1,295.10