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 $94.37   12.559%   $106.2219   $106.22   $106.20   $106.20  
  Purchase #2 $90.84   3.659%   $94.1638   $94.16   $94.15   $94.20  
  Purchase #3 $55.34   9.390%   $60.5364   $60.54   $60.55   $60.50  
  Purchase #4 $26.34   5.859%   $27.8833   $27.88   $27.90   $27.90  
  Purchase #5 $212.27   5.339%   $223.6031   $223.60   $223.60   $223.60  
  Purchase #6 $162.59   8.119%   $175.7907   $175.79   $175.80   $175.80  
  Purchase #7 $109.50   8.391%   $118.6881   $118.69   $118.70   $118.70  
  7 purchase totals = $751.25       $806.8873   $806.88   $806.90   $806.90