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 $244.29   4.137%   $254.3963   $254.40   $254.40   $254.40  
  Purchase #2 $108.86   12.831%   $122.8278   $122.83   $122.85   $122.80  
  Purchase #3 $59.89   13.170%   $67.7775   $67.78   $67.80   $67.80  
  Purchase #4 $175.58   3.121%   $181.0599   $181.06   $181.05   $181.10  
  Purchase #5 $129.68   13.183%   $146.7757   $146.78   $146.80   $146.80  
  Purchase #6 $126.90   5.305%   $133.632   $133.63   $133.65   $133.60  
  Purchase #7 $195.84   7.702%   $210.9236   $210.92   $210.90   $210.90  
  7 purchase totals = $1,041.04       $1,117.3928   $1,117.40   $1,117.45   $1,117.40