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 $86.73   8.323%   $93.9485   $93.95   $93.95   $93.90  
  Purchase #2 $163.71   12.133%   $183.5729   $183.57   $183.55   $183.60  
  Purchase #3 $88.49   8.775%   $96.255   $96.26   $96.25   $96.30  
  Purchase #4 $178.60   12.215%   $200.416   $200.42   $200.40   $200.40  
  Purchase #5 $243.85   8.298%   $264.0847   $264.08   $264.10   $264.10  
  Purchase #6 $146.64   5.420%   $154.5879   $154.59   $154.60   $154.60  
  Purchase #7 $183.98   5.201%   $193.5488   $193.55   $193.55   $193.50  
  7 purchase totals = $1,092.00       $1,186.4138   $1,186.42   $1,186.40   $1,186.40