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 $95.57   13.353%   $108.3315   $108.33   $108.35   $108.30  
  Purchase #2 $123.42   11.542%   $137.6651   $137.67   $137.65   $137.70  
  Purchase #3 $203.44   8.315%   $220.356   $220.36   $220.35   $220.40  
  Purchase #4 $149.80   11.662%   $167.2697   $167.27   $167.25   $167.30  
  Purchase #5 $243.71   4.784%   $255.3691   $255.37   $255.35   $255.40  
  Purchase #6 $19.44   6.423%   $20.6886   $20.69   $20.70   $20.70  
  Purchase #7 $14.94   5.616%   $15.779   $15.78   $15.80   $15.80  
  7 purchase totals = $850.32       $925.4590   $925.47   $925.45   $925.60