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 $109.70   12.632%   $123.5573   $123.56   $123.55   $123.60  
  Purchase #2 $181.36   3.578%   $187.8491   $187.85   $187.85   $187.80  
  Purchase #3 $233.72   3.278%   $241.3813   $241.38   $241.40   $241.40  
  Purchase #4 $237.27   5.369%   $250.009   $250.01   $250.00   $250.00  
  Purchase #5 $26.73   3.385%   $27.6348   $27.63   $27.65   $27.60  
  Purchase #6 $119.68   5.213%   $125.9189   $125.92   $125.90   $125.90  
  Purchase #7 $226.52   9.277%   $247.5343   $247.53   $247.55   $247.50  
  7 purchase totals = $1,134.98       $1,203.8847   $1,203.88   $1,203.90   $1,203.80