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 $55.33   11.757%   $61.8351   $61.84   $61.85   $61.80  
  Purchase #2 $221.63   10.253%   $244.3537   $244.35   $244.35   $244.40  
  Purchase #3 $196.33   13.851%   $223.5237   $223.52   $223.50   $223.50  
  Purchase #4 $43.79   6.788%   $46.7625   $46.76   $46.75   $46.80  
  Purchase #5 $250.95   9.770%   $275.4678   $275.47   $275.45   $275.50  
  Purchase #6 $45.28   12.416%   $50.902   $50.90   $50.90   $50.90  
  Purchase #7 $232.97   8.486%   $252.7398   $252.74   $252.75   $252.70  
  7 purchase totals = $1,046.28       $1,155.5846   $1,155.58   $1,155.55   $1,155.60