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 $93.44   3.513%   $96.7225   $96.72   $96.70   $96.70  
  Purchase #2 $160.99   12.742%   $181.5033   $181.50   $181.50   $181.50  
  Purchase #3 $167.78   5.859%   $177.6102   $177.61   $177.60   $177.60  
  Purchase #4 $182.31   3.317%   $188.3572   $188.36   $188.35   $188.40  
  Purchase #5 $35.36   13.794%   $40.2376   $40.24   $40.25   $40.20  
  Purchase #6 $226.60   6.347%   $240.9823   $240.98   $241.00   $241.00  
  Purchase #7 $110.89   13.809%   $126.2028   $126.20   $126.20   $126.20  
  7 purchase totals = $977.37       $1,051.6159   $1,051.61   $1,051.60   $1,051.60