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 $49.32   5.553%   $52.0587   $52.06   $52.05   $52.10  
  Purchase #2 $70.25   4.750%   $73.5869   $73.59   $73.60   $73.60  
  Purchase #3 $191.71   7.334%   $205.77   $205.77   $205.75   $205.80  
  Purchase #4 $235.83   7.352%   $253.1682   $253.17   $253.15   $253.20  
  Purchase #5 $167.47   11.393%   $186.5499   $186.55   $186.55   $186.50  
  Purchase #6 $131.62   4.871%   $138.0312   $138.03   $138.05   $138.00  
  Purchase #7 $177.65   9.415%   $194.3757   $194.38   $194.40   $194.40  
  7 purchase totals = $1,023.85       $1,103.5406   $1,103.55   $1,103.55   $1,103.60