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 $228.93   8.199%   $247.7   $247.70   $247.70   $247.70  
  Purchase #2 $107.57   9.453%   $117.7386   $117.74   $117.75   $117.70  
  Purchase #3 $166.81   5.541%   $176.0529   $176.05   $176.05   $176.10  
  Purchase #4 $204.29   3.726%   $211.9018   $211.90   $211.90   $211.90  
  Purchase #5 $73.40   7.645%   $79.0114   $79.01   $79.00   $79.00  
  Purchase #6 $85.65   7.117%   $91.7457   $91.75   $91.75   $91.70  
  Purchase #7 $60.99   13.684%   $69.3359   $69.34   $69.35   $69.30  
  7 purchase totals = $927.64       $993.4863   $993.49   $993.50   $993.40