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 $83.70   10.619%   $92.5881   $92.59   $92.60   $92.60  
  Purchase #2 $33.68   13.276%   $38.1514   $38.15   $38.15   $38.20  
  Purchase #3 $139.50   5.855%   $147.6677   $147.67   $147.65   $147.70  
  Purchase #4 $36.40   13.590%   $41.3468   $41.35   $41.35   $41.30  
  Purchase #5 $212.93   12.501%   $239.5484   $239.55   $239.55   $239.50  
  Purchase #6 $223.80   8.370%   $242.5321   $242.53   $242.55   $242.50  
  Purchase #7 $198.68   7.848%   $214.2724   $214.27   $214.25   $214.30  
  7 purchase totals = $928.69       $1,016.1069   $1,016.11   $1,016.10   $1,016.10