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 $93.97   10.227%   $103.5803   $103.58   $103.60   $103.60  
  Purchase #2 $207.41   9.255%   $226.6058   $226.61   $226.60   $226.60  
  Purchase #3 $66.36   10.653%   $73.4293   $73.43   $73.45   $73.40  
  Purchase #4 $122.88   9.604%   $134.6814   $134.68   $134.70   $134.70  
  Purchase #5 $205.50   12.286%   $230.7477   $230.75   $230.75   $230.70  
  Purchase #6 $88.25   13.618%   $100.2679   $100.27   $100.25   $100.30  
  Purchase #7 $163.42   13.179%   $184.9571   $184.96   $184.95   $185.00  
  7 purchase totals = $947.79       $1,054.2695   $1,054.28   $1,054.30   $1,054.30