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 $211.81   6.817%   $226.2491   $226.25   $226.25   $226.20  
  Purchase #2 $200.46   12.483%   $225.4834   $225.48   $225.50   $225.50  
  Purchase #3 $50.35   12.544%   $56.6659   $56.67   $56.65   $56.70  
  Purchase #4 $108.46   9.781%   $119.0685   $119.07   $119.05   $119.10  
  Purchase #5 $44.58   5.343%   $46.9619   $46.96   $46.95   $47.00  
  Purchase #6 $47.85   3.791%   $49.664   $49.66   $49.65   $49.70  
  Purchase #7 $43.38   3.569%   $44.9282   $44.93   $44.95   $44.90  
  7 purchase totals = $706.89       $769.0210   $769.02   $769.00   $769.10