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 $111.72   12.565%   $125.7576   $125.76   $125.75   $125.80  
  Purchase #2 $203.64   6.412%   $216.6974   $216.70   $216.70   $216.70  
  Purchase #3 $18.84   8.481%   $20.4378   $20.44   $20.45   $20.40  
  Purchase #4 $247.65   12.548%   $278.7251   $278.73   $278.75   $278.70  
  Purchase #5 $123.51   7.299%   $132.525   $132.53   $132.55   $132.50  
  Purchase #6 $181.85   13.339%   $206.107   $206.11   $206.10   $206.10  
  Purchase #7 $176.49   3.264%   $182.2506   $182.25   $182.25   $182.30  
  7 purchase totals = $1,063.70       $1,162.5005   $1,162.52   $1,162.55   $1,162.50