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 $25.78   3.145%   $26.5908   $26.59   $26.60   $26.60  
  Purchase #2 $216.51   7.561%   $232.8803   $232.88   $232.90   $232.90  
  Purchase #3 $197.63   8.688%   $214.8001   $214.80   $214.80   $214.80  
  Purchase #4 $106.88   9.700%   $117.2474   $117.25   $117.25   $117.20  
  Purchase #5 $197.53   7.865%   $213.0657   $213.07   $213.05   $213.10  
  Purchase #6 $244.54   4.279%   $255.0039   $255.00   $255.00   $255.00  
  Purchase #7 $87.51   9.718%   $96.0142   $96.01   $96.00   $96.00  
  7 purchase totals = $1,076.38       $1,155.6024   $1,155.60   $1,155.60   $1,155.60