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 $184.61   8.212%   $199.7702   $199.77   $199.75   $199.80  
  Purchase #2 $188.28   12.587%   $211.9788   $211.98   $212.00   $212.00  
  Purchase #3 $17.49   3.281%   $18.0638   $18.06   $18.05   $18.10  
  Purchase #4 $152.92   8.849%   $166.4519   $166.45   $166.45   $166.50  
  Purchase #5 $58.61   9.453%   $64.1504   $64.15   $64.15   $64.20  
  Purchase #6 $245.88   8.432%   $266.6126   $266.61   $266.60   $266.60  
  Purchase #7 $219.87   10.785%   $243.583   $243.58   $243.60   $243.60  
  7 purchase totals = $1,067.66       $1,170.6107   $1,170.60   $1,170.60   $1,170.80