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 $88.60   8.196%   $95.8617   $95.86   $95.85   $95.90  
  Purchase #2 $52.40   6.812%   $55.9695   $55.97   $55.95   $56.00  
  Purchase #3 $201.93   8.700%   $219.4979   $219.50   $219.50   $219.50  
  Purchase #4 $18.96   10.582%   $20.9663   $20.97   $20.95   $21.00  
  Purchase #5 $184.41   4.758%   $193.1842   $193.18   $193.20   $193.20  
  Purchase #6 $125.88   8.829%   $136.9939   $136.99   $137.00   $137.00  
  Purchase #7 $112.50   5.681%   $118.8911   $118.89   $118.90   $118.90  
  7 purchase totals = $784.68       $841.3646   $841.36   $841.35   $841.50