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 $176.70   5.716%   $186.8002   $186.80   $186.80   $186.80  
  Purchase #2 $53.61   13.321%   $60.7514   $60.75   $60.75   $60.80  
  Purchase #3 $104.50   11.546%   $116.5656   $116.57   $116.55   $116.60  
  Purchase #4 $84.69   9.726%   $92.9269   $92.93   $92.95   $92.90  
  Purchase #5 $72.34   11.637%   $80.7582   $80.76   $80.75   $80.80  
  Purchase #6 $130.67   3.237%   $134.8998   $134.90   $134.90   $134.90  
  Purchase #7 $127.27   5.459%   $134.2177   $134.22   $134.20   $134.20  
  7 purchase totals = $749.78       $806.9198   $806.93   $806.90   $807.00