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 $161.41   13.841%   $183.7508   $183.75   $183.75   $183.80  
  Purchase #2 $68.86   9.861%   $75.6503   $75.65   $75.65   $75.70  
  Purchase #3 $67.36   11.471%   $75.0869   $75.09   $75.10   $75.10  
  Purchase #4 $117.29   13.605%   $133.2473   $133.25   $133.25   $133.20  
  Purchase #5 $129.63   4.789%   $135.838   $135.84   $135.85   $135.80  
  Purchase #6 $145.76   5.638%   $153.9779   $153.98   $154.00   $154.00  
  Purchase #7 $131.76   4.364%   $137.51   $137.51   $137.50   $137.50  
  7 purchase totals = $822.07       $895.0612   $895.07   $895.10   $895.10