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 $216.38   10.686%   $239.5024   $239.50   $239.50   $239.50  
  Purchase #2 $190.48   9.568%   $208.7051   $208.71   $208.70   $208.70  
  Purchase #3 $131.56   9.236%   $143.7109   $143.71   $143.70   $143.70  
  Purchase #4 $143.38   11.840%   $160.3562   $160.36   $160.35   $160.40  
  Purchase #5 $165.36   11.455%   $184.302   $184.30   $184.30   $184.30  
  Purchase #6 $130.85   9.319%   $143.0439   $143.04   $143.05   $143.00  
  Purchase #7 $202.28   5.117%   $212.6307   $212.63   $212.65   $212.60  
  7 purchase totals = $1,180.29       $1,292.2512   $1,292.25   $1,292.25   $1,292.20