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 $65.36   12.838%   $73.7509   $73.75   $73.75   $73.80  
  Purchase #2 $206.69   11.103%   $229.6388   $229.64   $229.65   $229.60  
  Purchase #3 $213.67   4.456%   $223.1911   $223.19   $223.20   $223.20  
  Purchase #4 $41.93   8.235%   $45.3829   $45.38   $45.40   $45.40  
  Purchase #5 $54.75   13.850%   $62.3329   $62.33   $62.35   $62.30  
  Purchase #6 $174.91   13.315%   $198.1993   $198.20   $198.20   $198.20  
  Purchase #7 $230.40   6.533%   $245.452   $245.45   $245.45   $245.50  
  7 purchase totals = $987.71       $1,077.9479   $1,077.94   $1,078.00   $1,078.00