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 $167.37   10.814%   $185.4694   $185.47   $185.45   $185.50  
  Purchase #2 $30.48   10.346%   $33.6335   $33.63   $33.65   $33.60  
  Purchase #3 $192.43   3.257%   $198.6974   $198.70   $198.70   $198.70  
  Purchase #4 $69.78   8.831%   $75.9423   $75.94   $75.95   $75.90  
  Purchase #5 $234.92   10.503%   $259.5936   $259.59   $259.60   $259.60  
  Purchase #6 $59.65   12.263%   $66.9649   $66.96   $66.95   $67.00  
  Purchase #7 $57.92   5.649%   $61.1919   $61.19   $61.20   $61.20  
  7 purchase totals = $812.55       $881.4930   $881.48   $881.50   $881.50