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 $27.93   11.348%   $31.0995   $31.10   $31.10   $31.10  
  Purchase #2 $218.62   7.504%   $235.0252   $235.03   $235.05   $235.00  
  Purchase #3 $97.46   9.379%   $106.6008   $106.60   $106.60   $106.60  
  Purchase #4 $235.71   13.504%   $267.5403   $267.54   $267.55   $267.50  
  Purchase #5 $64.97   13.147%   $73.5116   $73.51   $73.50   $73.50  
  Purchase #6 $197.59   3.586%   $204.6756   $204.68   $204.70   $204.70  
  Purchase #7 $33.77   8.482%   $36.6344   $36.63   $36.65   $36.60  
  7 purchase totals = $876.05       $955.0874   $955.09   $955.15   $955.00