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 $39.85   9.453%   $43.617   $43.62   $43.60   $43.60  
  Purchase #2 $242.86   5.344%   $255.8384   $255.84   $255.85   $255.80  
  Purchase #3 $167.34   11.705%   $186.9271   $186.93   $186.95   $186.90  
  Purchase #4 $131.68   12.153%   $147.6831   $147.68   $147.70   $147.70  
  Purchase #5 $249.99   5.211%   $263.017   $263.02   $263.00   $263.00  
  Purchase #6 $144.49   6.331%   $153.6377   $153.64   $153.65   $153.60  
  Purchase #7 $24.92   11.686%   $27.8322   $27.83   $27.85   $27.80  
  7 purchase totals = $1,001.13       $1,078.5525   $1,078.56   $1,078.60   $1,078.40