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 $24.51   8.393%   $26.5671   $26.57   $26.55   $26.60  
  Purchase #2 $234.49   7.486%   $252.0439   $252.04   $252.05   $252.00  
  Purchase #3 $71.48   4.581%   $74.7545   $74.75   $74.75   $74.80  
  Purchase #4 $84.26   10.639%   $93.2244   $93.22   $93.20   $93.20  
  Purchase #5 $244.60   11.551%   $272.8537   $272.85   $272.85   $272.90  
  Purchase #6 $206.78   11.477%   $230.5121   $230.51   $230.50   $230.50  
  Purchase #7 $89.84   8.248%   $97.25   $97.25   $97.25   $97.30  
  7 purchase totals = $955.96       $1,047.2057   $1,047.19   $1,047.15   $1,047.30