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 $45.50   5.203%   $47.8674   $47.87   $47.85   $47.90  
  Purchase #2 $239.55   5.510%   $252.7492   $252.75   $252.75   $252.70  
  Purchase #3 $29.28   8.613%   $31.8019   $31.80   $31.80   $31.80  
  Purchase #4 $80.65   8.649%   $87.6254   $87.63   $87.65   $87.60  
  Purchase #5 $37.48   12.780%   $42.2699   $42.27   $42.25   $42.30  
  Purchase #6 $18.48   7.427%   $19.8525   $19.85   $19.85   $19.90  
  Purchase #7 $138.67   12.503%   $156.0079   $156.01   $156.00   $156.00  
  7 purchase totals = $589.61       $638.1742   $638.18   $638.15   $638.20