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 $95.91   7.747%   $103.3401   $103.34   $103.35   $103.30  
  Purchase #2 $170.96   11.634%   $190.8495   $190.85   $190.85   $190.80  
  Purchase #3 $184.58   12.597%   $207.8315   $207.83   $207.85   $207.80  
  Purchase #4 $90.96   8.787%   $98.9527   $98.95   $98.95   $99.00  
  Purchase #5 $19.98   3.211%   $20.6216   $20.62   $20.60   $20.60  
  Purchase #6 $64.50   3.629%   $66.8407   $66.84   $66.85   $66.80  
  Purchase #7 $187.75   10.714%   $207.8655   $207.87   $207.85   $207.90  
  7 purchase totals = $814.64       $896.3016   $896.30   $896.30   $896.20