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 $110.98   6.592%   $118.2958   $118.30   $118.30   $118.30  
  Purchase #2 $247.88   12.371%   $278.5452   $278.55   $278.55   $278.50  
  Purchase #3 $168.49   13.471%   $191.1873   $191.19   $191.20   $191.20  
  Purchase #4 $127.25   12.700%   $143.4108   $143.41   $143.40   $143.40  
  Purchase #5 $48.50   4.508%   $50.6864   $50.69   $50.70   $50.70  
  Purchase #6 $238.63   5.216%   $251.0769   $251.08   $251.10   $251.10  
  Purchase #7 $59.99   11.297%   $66.7671   $66.77   $66.75   $66.80  
  7 purchase totals = $1,001.72       $1,099.9695   $1,099.99   $1,100.00   $1,100.00