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 $227.59   7.742%   $245.21   $245.21   $245.20   $245.20  
  Purchase #2 $140.53   6.689%   $149.9301   $149.93   $149.95   $149.90  
  Purchase #3 $49.67   11.545%   $55.4044   $55.40   $55.40   $55.40  
  Purchase #4 $155.85   3.653%   $161.5432   $161.54   $161.55   $161.50  
  Purchase #5 $129.93   10.300%   $143.3128   $143.31   $143.30   $143.30  
  Purchase #6 $230.32   9.738%   $252.7486   $252.75   $252.75   $252.70  
  Purchase #7 $32.71   8.614%   $35.5276   $35.53   $35.55   $35.50  
  7 purchase totals = $966.60       $1,043.6767   $1,043.67   $1,043.70   $1,043.50