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 $239.78   11.855%   $268.2059   $268.21   $268.20   $268.20  
  Purchase #2 $154.56   8.247%   $167.3066   $167.31   $167.30   $167.30  
  Purchase #3 $225.95   9.281%   $246.9204   $246.92   $246.90   $246.90  
  Purchase #4 $97.68   11.150%   $108.5713   $108.57   $108.55   $108.60  
  Purchase #5 $208.55   6.698%   $222.5187   $222.52   $222.50   $222.50  
  Purchase #6 $57.33   12.441%   $64.4624   $64.46   $64.45   $64.50  
  Purchase #7 $195.79   5.592%   $206.7386   $206.74   $206.75   $206.70  
  7 purchase totals = $1,179.64       $1,284.7239   $1,284.73   $1,284.65   $1,284.70