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 $68.29   5.214%   $71.8506   $71.85   $71.85   $71.90  
  Purchase #2 $162.89   7.277%   $174.7435   $174.74   $174.75   $174.70  
  Purchase #3 $161.60   5.792%   $170.9599   $170.96   $170.95   $171.00  
  Purchase #4 $246.47   4.865%   $258.4608   $258.46   $258.45   $258.50  
  Purchase #5 $201.52   6.530%   $214.6793   $214.68   $214.70   $214.70  
  Purchase #6 $55.34   9.535%   $60.6167   $60.62   $60.60   $60.60  
  Purchase #7 $52.92   10.762%   $58.6153   $58.62   $58.60   $58.60  
  7 purchase totals = $949.03       $1,009.9261   $1,009.93   $1,009.90   $1,010.00