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 $69.38   7.541%   $74.6119   $74.61   $74.60   $74.60  
  Purchase #2 $171.81   9.775%   $188.6044   $188.60   $188.60   $188.60  
  Purchase #3 $25.98   7.647%   $27.9667   $27.97   $27.95   $28.00  
  Purchase #4 $214.37   11.454%   $238.9239   $238.92   $238.90   $238.90  
  Purchase #5 $103.52   8.722%   $112.549   $112.55   $112.55   $112.50  
  Purchase #6 $236.56   4.740%   $247.7729   $247.77   $247.75   $247.80  
  Purchase #7 $168.61   10.621%   $186.5181   $186.52   $186.50   $186.50  
  7 purchase totals = $990.23       $1,076.9469   $1,076.94   $1,076.85   $1,076.90