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 $88.95   8.547%   $96.5526   $96.55   $96.55   $96.60  
  Purchase #2 $9.74   7.845%   $10.5041   $10.50   $10.50   $10.50  
  Purchase #3 $197.98   10.126%   $218.0275   $218.03   $218.05   $218.00  
  Purchase #4 $64.60   5.482%   $68.1414   $68.14   $68.15   $68.10  
  Purchase #5 $168.38   12.386%   $189.2355   $189.24   $189.25   $189.20  
  Purchase #6 $81.59   4.427%   $85.202   $85.20   $85.20   $85.20  
  Purchase #7 $155.55   11.606%   $173.6031   $173.60   $173.60   $173.60  
  7 purchase totals = $766.79       $841.2662   $841.26   $841.30   $841.20