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 $76.79   11.821%   $85.8673   $85.87   $85.85   $85.90  
  Purchase #2 $179.67   3.436%   $185.8435   $185.84   $185.85   $185.80  
  Purchase #3 $105.94   10.606%   $117.176   $117.18   $117.20   $117.20  
  Purchase #4 $197.35   4.826%   $206.8741   $206.87   $206.85   $206.90  
  Purchase #5 $43.53   12.171%   $48.828   $48.83   $48.85   $48.80  
  Purchase #6 $21.86   12.440%   $24.5794   $24.58   $24.60   $24.60  
  Purchase #7 $202.33   13.134%   $228.904   $228.90   $228.90   $228.90  
  7 purchase totals = $827.47       $898.0723   $898.07   $898.10   $898.10