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 $14.44   5.591%   $15.2473   $15.25   $15.25   $15.20  
  Purchase #2 $205.63   3.399%   $212.6194   $212.62   $212.60   $212.60  
  Purchase #3 $162.54   13.415%   $184.3447   $184.34   $184.35   $184.30  
  Purchase #4 $9.61   4.824%   $10.0736   $10.07   $10.05   $10.10  
  Purchase #5 $217.35   3.373%   $224.6812   $224.68   $224.70   $224.70  
  Purchase #6 $167.65   8.497%   $181.8952   $181.90   $181.90   $181.90  
  Purchase #7 $200.48   13.764%   $228.0741   $228.07   $228.05   $228.10  
  7 purchase totals = $977.70       $1,056.9355   $1,056.93   $1,056.90   $1,056.90