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 $201.34   11.607%   $224.7095   $224.71   $224.70   $224.70  
  Purchase #2 $62.57   5.574%   $66.0577   $66.06   $66.05   $66.10  
  Purchase #3 $168.39   12.118%   $188.7955   $188.80   $188.80   $188.80  
  Purchase #4 $37.56   5.189%   $39.509   $39.51   $39.50   $39.50  
  Purchase #5 $66.35   7.116%   $71.0715   $71.07   $71.05   $71.10  
  Purchase #6 $215.68   8.196%   $233.3571   $233.36   $233.35   $233.40  
  Purchase #7 $171.49   13.689%   $194.9653   $194.97   $194.95   $195.00  
  7 purchase totals = $923.38       $1,018.4656   $1,018.48   $1,018.40   $1,018.60