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 $171.59   8.235%   $185.7204   $185.72   $185.70   $185.70  
  Purchase #2 $209.79   4.277%   $218.7627   $218.76   $218.75   $218.80  
  Purchase #3 $102.46   12.483%   $115.2501   $115.25   $115.25   $115.30  
  Purchase #4 $162.36   7.326%   $174.2545   $174.25   $174.25   $174.30  
  Purchase #5 $115.52   8.142%   $124.9256   $124.93   $124.95   $124.90  
  Purchase #6 $141.41   12.760%   $159.4539   $159.45   $159.45   $159.50  
  Purchase #7 $43.68   3.503%   $45.2101   $45.21   $45.20   $45.20  
  7 purchase totals = $946.81       $1,023.5773   $1,023.57   $1,023.55   $1,023.70