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 $231.85   9.636%   $254.1911   $254.19   $254.20   $254.20  
  Purchase #2 $232.98   8.748%   $253.3611   $253.36   $253.35   $253.40  
  Purchase #3 $186.44   9.432%   $204.025   $204.03   $204.05   $204.00  
  Purchase #4 $175.67   6.380%   $186.8777   $186.88   $186.90   $186.90  
  Purchase #5 $51.80   13.795%   $58.9458   $58.95   $58.95   $58.90  
  Purchase #6 $99.59   13.120%   $112.6562   $112.66   $112.65   $112.70  
  Purchase #7 $96.47   3.770%   $100.1069   $100.11   $100.10   $100.10  
  7 purchase totals = $1,074.80       $1,170.1638   $1,170.18   $1,170.20   $1,170.20