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 $24.44   9.134%   $26.6723   $26.67   $26.65   $26.70  
  Purchase #2 $237.98   3.855%   $247.1541   $247.15   $247.15   $247.20  
  Purchase #3 $161.43   6.252%   $171.5226   $171.52   $171.50   $171.50  
  Purchase #4 $204.58   9.183%   $223.3666   $223.37   $223.35   $223.40  
  Purchase #5 $246.75   6.392%   $262.5223   $262.52   $262.50   $262.50  
  Purchase #6 $60.50   7.197%   $64.8542   $64.85   $64.85   $64.90  
  Purchase #7 $234.72   6.618%   $250.2538   $250.25   $250.25   $250.30  
  7 purchase totals = $1,170.40       $1,246.3459   $1,246.33   $1,246.25   $1,246.50