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 $167.36   9.262%   $182.8609   $182.86   $182.85   $182.90  
  Purchase #2 $250.80   12.301%   $281.6509   $281.65   $281.65   $281.70  
  Purchase #3 $171.62   4.623%   $179.554   $179.55   $179.55   $179.60  
  Purchase #4 $48.85   11.322%   $54.3808   $54.38   $54.40   $54.40  
  Purchase #5 $242.74   5.697%   $256.5689   $256.57   $256.55   $256.60  
  Purchase #6 $243.70   13.787%   $277.2989   $277.30   $277.30   $277.30  
  Purchase #7 $109.95   3.600%   $113.9082   $113.91   $113.90   $113.90  
  7 purchase totals = $1,235.02       $1,346.2226   $1,346.22   $1,346.20   $1,346.40